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Probing Question: When did the snake lose its legs?

Probing Question: When did the snake lose its legs?

Joseph Gyekis

November 07, 2005

Charles Fergus

It has long been known that snakes are descendants of lizards, but whether snakes lost their legs while living in the sea or on land has been a matter of great debate among evolutionary biologists. Only one group of marine lizards, the mosasaurs, lived during the Cretaceous period when snakes first appear in the fossil record. These extinct relatives of the Komodo dragon have a skeleton that is much like a snake's (albeit 30 feet long), provoking some researchers to speculate that the snake family descended from mosasaurs. Penn State biologists Nicolas Vidal and S. Blair Hedges came to a different conclusion after comparing specific genes across a wide variety of snakes and lizards. "Although these genes have the same function in each species—and so, by definition, are the same gene—their structure in each species is slightly different because of mutations that have developed over time," Hedges says. Results show that snake genes match up much better with land-dwelling lizard lineages than they do with Komodo dragons, key evidence to support the terrestrial origin hypothesis. The finding also grants credibility to another theory: that without legs, snake ancestors could fit into narrower burrows, opening up new avenues for the pursuit of small prey.

S. Blair Hedges, Ph.D., professor of biology, can be reached at sbh1@psu.edu.